"BF3 does auto OC your card to maximum performance". There is no such thing. Maximum performance is always one step higher than your current performance level. If it tried to achieve "maximum performance", it would overclock your card to infinity until it crashed. Are you saying that BF3 has a built in artifact scanner to determine when your card is artifacting so that it can back the overclock down to this "maximum performance" level?
You see? Maximum performance is relative. I have never seen anyone take overclocking into their hands other than the end-user or the video card board distributor. The video card board distributor does it through thorough testing and adds it as a marketing sales point. BF3 takes it into their own hands? I can't believe it.
I just started up GPU-z. I clicked on the Sensors tab and selected "Continue refreshing this screen while GPU-Z is in the background". Then I went to battlelog and started a round. I played for about 5 minutes and then exited the game. I checked GPU-Z. Not even 1MHz overclock on anything.
Two GTX 580s with no overclocking software installed. (no EVGA Precision, MSI Afterburner, or NVIDIA System Tools installed to screw with my results)